<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>

        // 使用 const 关键字定义的常量，一旦被定义之后就不能再修改。
        const greeting = 'Hello World!';
            greeting = '你好，世界！';

        console.log(greeting)

    </script>
</body>
</html>